Strip cooling control for flexible production of galvanized flat steel

The work is devoted to the problem of flexible small-scale production of galvanized steel of various sizes on a continuous hot-dip galvanizing unit with varying productivity. The main focus is on the heat treatment of steel strip, the requirements for which limit productivity. In conditions of disturbances, it is necessary to proactively control the heat treatment using models, or to reduce the speed of the strip to ensure that the requirements are met. Unlike most of the works that focus on heat control, this work focuses on strip cooling. Based on the analysis of production data of the Magnitogorsk Iron and Steel Works, it is shown that violation of the cooling requirements leads to the appearance of defects in the zinc coating. Dependence of the probability of defects occurrence on the strip temperature is given. Problems of cooling predictive control are formulated using models in the absence of temperature control of the cooling section cavity. For each of the tasks, the model structure and the method of its tuning are determined according to the data accumulated over a significant period of the unit operation under conditions of uncontrolled systematic disturbances. The structure of the cooling control system is proposed by estimation of the cooling section cavity temperature as a controlled variable. The temperature estimate is determined from the model. The lack of measurement of the cooling section cavity temperature is not a problem then varying productivity. The results of the models tuning are presented according to the data of the Magnitogorsk Iron and Steel Works continuous hot-dip galvanizing unit. The proposed structures of the models and methods for their adjustment can be applied in the development of models for metal heating in furnaces.

Influence of Segmented Rolls on Homogeneity of Cooling in Continuous Casting

This paper deals with secondary cooling in a continuous caster. In particular, it deals with cooling inhomogeneity caused by spray arrangement and segmented rolls used for leading the strand. The cooling section is placed under the mold. Segmented rolls are supported by bearings in several places across the strand. Sprayed water can flow in the gaps between rolls where the bearing pocket is located. The main question that was experimentally studied is how this geometry with segmented rolls can influence homogeneity of cooling. Two experimental approaches developed for this study were applied, and both used full-scale geometrical configuration. The first one was a cold test where water flow and water distribution were observed using a transparent board with the studied surface structures (rollers and bearing pockets) and four spraying nozzles. The second one was a cooling test using a heated steel plate with rolls and bearing pockets. Cooling homogeneity was studied based on the temperature distribution on the rear side of the sample, which was recorded using an infrared camera. Homogeneity of cooling distribution was experimentally studied for three levels of cooling intensity that are used in typical cooling sections in plants. The hot tests showed that the bearing pockets do not provide significant cooling inhomogeneity despite the fact that a large amount of water flows through the gap between the rollers (which has been observed in cold tests).

Characterization of Graded Subsurface Zones in Industrial Case-Hardening Using a Non-Destructive Testing System

For process monitoring and quality assurance of case-hardened components, the determination of the case-hardening depth in the manufacturing process after hardening of the subsurface layer is a quality verification that is often required in industry. Currently, these quality assurance tests can only be realized with destructive measures. During case-hardening, the essential microstructural formation, and thus the key component properties are developed during the heat treatment in the cooling section. The testing technique used in the present study is based on the analysis of harmonic signals of eddy current testing. The aim of this project was to achieve an early identification of incorrect cooling processes in the case of a known transformation behaviour of the components during cooling. The data collected in the industrial hardening process show that an evaluation of the carburizing process on the basis of the case-hardening depth can be carried out non-destructively during component cooling and in the cooled state with the use of eddy current technology.

Effects of the Wall Properties on the Cooling Efficiency in a Thermosyphon Containing PCM Suspensions

This study explores the effects of pipe wall properties (thermal conductivity k and wall thickness tw) on the heat transfer performance of a rectangular thermosyphon with a phase change material (PCM) suspension and a geometric configuration (aspect ratio = 1; dimensionless heating section length = 0.8; dimensionless relative elevation between the cooling and the heating sections = 2) that ensures the optimum heat transfer efficiency in the cooling section. The following parameter ranges are studied: the dimensionless loop wall thickness (0 to 0.5), wall-to-fluid thermal conductivity ratio (0.1 to 100), modified Rayleigh number (1010 to 1011), and volumetric fraction of PCM particles (0 to 10%). The results show that appropriate selection of k and tw can lead to improved heat transfer effectiveness in the cooling section of the PCM suspension-containing rectangular thermosyphon.

Combined Brayton, Inverse Brayton and Steam Cycles Power Plant

Nowadays, more significant effort is needed to improve power generation efficiency to respond to environmental concerns. Several innovative technological options are under development and, among them, the integration of different energy systems is one remarkable opportunity. In this work, a combination of three different thermodynamic cycles has been proposed and studied: an Inverted Brayton cycle (IBC) is used to exploit the exhaust gas enthalpy of a Brayton-Joule cycle and a Steam Power Plant is bottomed to the Inverted Brayton Cycle, in order to recover the high thermal power wasted in its cooling section. In other words, a quite conventional natural gas combined cycle power plant is repowered introducing the Inverted Brayton Cycle to exploit the gas thermal power between the gas turbine and the heat recovery steam generator. In this integration, each parameter has a strong influence on the overall performance of the system: pressure ratio of the gas cycle, sub-atmospheric pressure of the inverted one, turbines inlet and outlet temperatures and heat recovery grade in the bottom steam section have been investigated in order to optimize the working conditions and find a best operating point. A post combustion opportunity was also considered, exploring for the best position to place it along the gases path and to get the maximum additional power through the repowering intervention.

The Influence of Turbulence and Reynolds Number on Multiple Slot Film Cooling Over the Suction Surface

Developing robust film cooling protection on the suction surface of a vane is critical to managing the high heat loads which exist there. Suction surface film cooling often produces high levels of film cooling but can be influenced by secondary flows and some dissipation due to free-stream turbulence. Directly downstream from suction surface film cooling, heat loads are often significantly mitigated and internal cooling levels can be modest. One thermodynamically efficient way to cool the suction surface of a vane is with a counter cooling scheme. This combined internal/external cooling method moves cooling air in a direction opposite to the external flow through an internal convection array. The coolant is then discharged upstream where the high level of film cooling can offset the reduced cooling potential of the spent cooling air. The present suction surface film cooling arrangement combines a slot film cooling discharge on the near suction surface from an incremental impingement cooling method with a second from a counter cooling section. A second counter cooling section is added further downstream on the suction surface. The internal cooling plenums replicate the geometry of the cooling methods to ensure the fluid dynamics of the flow discharging from the slots are representative of the actual internal cooling geometry. These film cooling flows have been tested at blowing ratios of 0.5 and 1.0 for the initial slot and blowing ratios of 0.15 and 0.3 for the two downstream slots. The measurements have been taken at exit chord Reynolds numbers of 500,000, 1,000,000, and 2,000,000 with inlet turbulence levels ranging from 0.7% to 12.6%. Film cooling effectiveness measurements were acquired using both thermocouples and infrared thermography. The infrared thermography shows the influence of secondary flows on film cooling coverage near the suction surface endwall junction. The film cooling effectiveness results at varied blowing ratios, turbulence levels and Reynolds numbers document the impact of these major variables on suction surface slot film cooling. The results provide a consistent picture of the slot film cooling for the present three slot arrangement on the suction surface and they support the development of an advanced double wall cooling method.

Effects of the Aspect Ratio of a Rectangular Thermosyphon on Its Thermal Performance

The natural convection behaviors of rectangular thermosyphons with different aspect ratios were experimentally analyzed in this study. The experimental model consisted of a loop body, a heating section, a cooling section, and adiabatic sections. The heating and cooling sections were located in the vertical portions of the rectangular loop. The length of the vertical cooling section and the lengths of the upper and lower adiabatic sections were fixed at 300 mm and 200 mm, respectively. The inner diameter of the loop was fixed at 11 mm, and the cooling end temperature was 30 °C. The relevant parameters and their ranges were as follows: The aspect ratios were 6, 4.5, and 3.5 (with potential differences of 41, 27, and 18, respectively, between the cold and hot ends), and the input thermal power ranged from 30 to 60 W (with a heat flux of 600 to 3800 W/m2). The results show that it is feasible to obtain solar heat gain by installing a rectangular thermosyphon inside the metal curtain wall and that increasing the height of the opaque part of the metal curtain wall can increase the aspect ratio of the rectangular thermosyphon installed inside the wall and thus improve the heat transfer efficiency.

Experimental Observation of Natural Convection Heat Transfer Performance of a Rectangular Thermosyphon

This study experimentally investigates the natural convection heat transfer performance of a rectangular thermosyphon with an aspect ratio of 3.5. The experimental model is divided into a loop body, a heating section, a cooling section, and two adiabatic sections. The heating section and the cooling section are located in the vertical legs of the rectangular loop. The length of the vertical heating section and the length of the upper and lower horizontal insulation sections are 700 mm and 200 mm, respectively, and the inner diameter of the loop is 11 mm. The relevant parameters and their ranges are as follows: the input thermal power is 30–60 W (with a heat flux in the range of 60–3800 W/m2); the temperature in the cooling section is 30, 40, or 50 °C; and the potential difference between the hot and cold sections is 5, 11, or 18 for the cooling section lengths of 60, 45, and 30 cm, respectively. The results indicate that the value of the dimensionless heat transfer coefficient, the Nusselt number, is generally between 5 and 10. The heating power is the main factor affecting the natural convection intensity of the thermosyphon.

Performance Analysis of a Solid Oxide Fuel Cell-Gasifier Integrated System in Co-Trigenerative Arrangement

The use of renewable sources, such as woody biomass waste, for energy purposes helps to reduce the consumption of fossil fuels and therefore the production of associated pollutants and greenhouse gases. Solid oxide fuel cells (SOFCs) are devices that convert the chemical energy of a product gas produced by a gasifier of biomass waste, before being suitably purified, directly into electric energy, with conversion efficiency, which is higher than that of other conventional energy systems. Since they operate at high temperature, they make available also thermal energy, which can be used for co- and tri-generation purposes. This paper aims at studying the arrangement of a complete trigenerative energy system composed of a gasifier of waste biomass; an energy unit represented by a SOFC system; an absorption cooling section for the conversion into cooling energy of the waste heat. In its layout, the SOFC energy unit considers the anode off gas recirculation, a postcombustor to energize the exhaust stream, and a preheater for the fresh gases entering. The integrated plant is completed by means of batteries for electric energy storage and hot water tanks and thermal energy storage. An ad hoc developed numerical modeling is used to choose the working point of the SOFC energy system at which to operate it and to analyze its energy behavior under syngas feeding. Two biomass-derived syngas are analyzed: one from woody biomass and one from urban solid waste gasification. Hence, the entire integrated plant is analyzed for both feeding types. The energy analysis of the integrated SOFC/gasifier is carried out based on a fixed quantity of biomass waste to be processed in an existing gasifier. Then, the design of the SOFC energy section is carried out. The integrated plant is then applied to a case study to satisfy the energy needs of a user of the tertiary sector. Therefore, based on this, the procedure continues with sizing the cooling section for the cooling power delivery in the warm season, the batteries to store the electric energy to be delivered, and the hot water tanks for the thermal energy storage to be delivered as heat when necessary or to feed the absorption cooling plant. The integrated SOFC/Gasifier defined can be considered as a high-efficiency tri-generator capable of accomplishing an energy valorization of high quality waste biomass.